The present invention relates to a notch forming device for forming a notch on the edge of a sheet having been conveyed, and a bookbinding apparatus and bookbinding system for stacking plural sheets with notches formed thereon into a sheet bundle and for producing a booklet by gluing the sheet bundle with adhesive.
Various kinds of techniques have been proposed to stack plural sheets with images formed thereon into a sheet bundle and produce a booklet by gluing the sheet bundle and a cover sheet with an adhesive. For example, in a bookbinding system including an image forming apparatus such as a copying machine and a printer, plural sheets on which images are formed by the image forming apparatus are stacked automatically into a sheet bundle, and a cover sheet is pasted onto the sheet bundle with an adhesive to produce a booklet.
Here, a general procedure to produce a booklet in this bookbinding system will be explained. First, a plurality of sheets on which images are formed are collected and aligned into a sheet bundle. Next, an adhesive is coated on a spine of the collected aligned sheet bundle. Then, a cover sheet is conveyed and stopped at a predetermined position, and the cover sheet is pasted onto the spine of the sheet bundle. In this procedure, a plurality of sheets and a cover sheet are made in one body, whereby a booklet is produced.
FIGS. 17a and 17b each shows an example of a booklet constituted by a sheet bundle and a cover sheet.
FIG. 17a shows a condition that a cover sheet K is not folded, and FIG. 17b shows a condition that the cover sheet K is folded. As shown in FIG. 17a, the pine Sb of a sheet bundle Sa is coated with an adhesive, and the sheet bundle Sa is shifted in the arrowed direction and is joined with the cover sheet K. Thereafter, the sheet bundle Sa is covered in the form of capital U by the cover sheet K. On the final condition of a booklet, as shown in FIG. 17b, the side edge Se of the sheet bundle Sa is aligned with the side edge Ke of the cover sheet K.
Here, in some cases, there is a problem that if the spine Sb of a sheet bundle Sa is coated with an adhesive without a special treatment and the sheet bundle Sa is joined with a cover sheet K to produce a booklet, a jointing force between the sheet bundle Sa and the cover sheet K is not secured sufficiently and a part of sheets falls out of the produced booklet.
In order to solve the above problem, as shown in FIG. 18, notches V are formed on the edge of a sheet S. When a plurality of sheets with such notches formed on their edges are stacked into a sheet bundle Sa, notch grooves Va constituted by the notches V are formed on the spine Sb of the sheet bundle Sa as shown in FIG. 19a. For example, as shown in FIG. 19b which shows the condition of the spine Sb of the sheet bundle Sa viewed from the direction of X in FIG. 19a, a notch grooves Va are formed in a vertical straight form.
In this way, with the structure that notches V are formed on the edge of sheets S, a space to receive a sufficient amount of an adhesive is secured between the spine of a sheet bundle and a cover sheet, whereby a sufficient adhesive force can be secured between the spine of a sheet bundle and a cover sheet. A technique to form notches V on the edge of sheets S is disclosed by Japanese Patent Unexamined Publication No. 2001-261221 and Japanese Patent Unexamined Publication No. 2007-62145. In these publications, a notch forming section is provided on a conveying path to convey a sheet with images formed thereon such that notches V as shown in FIG. 18 are formed automatically on the edge of sheets S.
The positions of notches V formed on sheets S can be set up variously, for example, it may be considered that the positions of notches V are shifted for each sheet in such a way that the notch grooves Va constituted by the notches V are shaped into a slant form as shown in FIG. 20a. With this structure that the positions of notches V are shifted for each sheet, an adhesive is introduced into the shifted regions between sheets indicated with oblique lines in FIG. 20b, whereby an adhesive strength between the sheets can be secured.
Here, a study is made on the case where plural booklets are produced continuously by the form of a sheet bundle in which notch grooves Va with a slant form are formed. For example, it is presupposed that plural sheet bundles Sa in which notch grooves Va are formed in a zigzag bent form as shown in FIGS. 21a through 21c is produced successively and plural booklets are produced continuously by pasting a cover sheet on each of the plural sheet bundles Sa. The sheet bundle Sa shown in FIG. 21a is a sheet bundle constituting the first booklet, the sheet bundle Sa shown in FIG. 21b is a sheet bundle constituting the second booklet, and the sheet bundle Sa shown in FIG. 21c is a sheet bundle constituting the third booklet. Here, in each sheet bundle, a sheet of the leading page is positioned at the lowermost position and a sheet of the last page is positioned at the uppermost position.
The positions of notches in the last page of a sheet bundle Sa shown in FIG. 21a are the same as the positions of notches in the leading page of a sheet bundle Sa shown in FIG. 21b. Further, the positions of notches in the last page of a sheet bundle Sa shown in FIG. 21b are the same as the positions of notches in the leading page of a sheet bundle Sa shown in FIG. 21c. Namely, in plural sheet bundles Sa produced successively, the positions of notches in the last page of the previous sheet bundle are the same as the positions of notches in the leading page of the next sheet bundle. Therefore, the positions of notches in the leading page of the sheet bundle Sa shown in FIG. 21a and FIG. 21c are different from the positions of notches in the leading page of the sheet bundle Sa shown in FIG. 21b. 
As shown in FIGS. 21a through 21c, if the positions of notches in the leading page of each sheet bundle Sa are not the same positions, since a notch grooves Va in a zigzag bent form stats from the positions of notches in the leading page, the form of the notch grooves Va in the sheet bundle Sa in FIG. 21a and FIG. 21c are different from that of the notch grooves Va in the sheet bundle Sa in FIG. 21b. 
In the case that a booklet is produces in such a way a cover sheet is pasted onto a sheet bundle Sa, since the notch grooves Va are covered with a cover sheet, the condition of the sheet bundle cannot be observed directly. However, for example, if a booklet is produced with a thin cover sheet, the form of notch grooves Va on the pine of a booklet can be observed through the thin cover sheet. Therefore, if the form of notch grooves Va are different among plural booklets produced successively as shown in FIGS. 21a through 21c, they look horrible. Further, if a booklet is produced in such a way that a sheet bundle Sa is merely coated with an adhesive without being covered with a cover sheet thereon, notch grooves Va are observed directly on the condition of the booklet, especially such a bad appearance is conspicuous.
Further, if the form of notch grooves Va are different among plural booklets, the positions on which a large amount of adhesive is adhered become different. Therefore, in the case that a cover sheet is pasted on a sheet bundle, an adhesive force between the cover sheet and the sheet bundle may become different among the plural booklets.